1. Field of the Invention
The invention relates to scaffolds which can be used as medical devices for guided tissue regeneration and repair and for the selective capture of cell populations from a cell source material.
2. Description of the Related Art
Scaffold technologies are known for use in dermal regeneration in chronic and acute wounds. A number of these technologies exploit the biological properties of relatively pure natural polymers such as collagen, silk, alginate, chitosan and hyaluronate extracted from animal or plant tissue. Others are based upon processed extracellular matrix (decellularized) materials which contain multiple natural macromolecules. An example of such a scaffold is Oasis® (Healthpoint Limited), a biologically derived extracellular matrix-based wound product comprised of porcine-derived acellular small intestine submucosa which contains type I collagen, glycosaminoglycans and some growth factors.
However, there are concerns over the use of natural polymers because of the potential pathogen transmission, immune reactions, poor handling, mechanical properties and less controlled biodegradability1.
The technique of electrospinning was first introduced in the early 1930's to fabricate industrial or household non-woven fabric products. In recent years, the technique has been utilised to form scaffolds of polymer fibres for use in tissue engineering. The technique involves forcing a natural or synthetic polymer solution through a capillary, forming a drop of the polymer solution at the tip and applying a large potential difference between the tip and a collection target. When the electric field overcomes the surface tension of the droplet, a polymer solution jet is initiated and accelerated towards the collection target. As the jet travels through the air, the solvent evaporates and a non-woven polymer fabric is formed on the target. Such fibrous fabrics, having an average fibre diameter in the micrometer or nanometer scale, have been used to fabricate complex three-dimensional scaffolds for use in tissue engineering applications.
It is widely accepted within the scientific community that scaffolds having fibres of a small diameter result in the greatest biological response, as evidenced by measuring cell adhesion and proliferation. This is considered to be as a result of the fibres providing a large surface area to which the cells can adhere and subsequently proliferate. As a strong correlation exists between fibre diameter and pore size, any scaffold having fibres of a small diameter will be also characterised by small pore size. This will however have a negative effect on the migration of the cells into the scaffold, potentially leading to a restricted regeneration of replacement tissue around the periphery of the scaffold, with the core of the scaffold being substantially acellular.
An unanticipated problem associated with many of the known electrospun scaffolds is that they become dimensionally unstable when incubated in aqueous solution at body temperature. This instability is measurable both macroscopically by scaffold shrinkage and microscopically by loss of initial fibrous architecture and reduction in initial pare size. Dimensionally unstable scaffolds will be of minimal use as their shrinkage can potentially have a significant impact on the behaviour of the scaffold and its interaction with the cellular environment.